Bio-based foams are moving into the mainstream of the construction/building industry and the protective packaging industry, this move is being driven by a need to replace petroleum based foams. Bio-based foams reduce carbon footprints, and the risk of unpredictable and increasing prices of fossil fuels based foams.
Starch-based foams, vegetables oil based polyurethane foams with addition of natural fibers with biodegradable or synthetic polymers were disclosed in the following: U.S. Pat. Nos. 5,308,879, 5,958,589, 5,266,368, WO 2006/133528 A2 and Liu et al. (2009, J. Forestry Research, 20(2): 161-164).
In the U.S. Pat. No. 4,386,119, discloses a wet process and apparatus for rendering cellulosic insulation particles fire-retardant through impregnation of a cellulosic insulating material, such as waste paper in finely divided form, with an aqueous solution of a non-hygroscopic fire retardant compositions, for example, boric acid is dissolved with a minimum amount of water as the impregnated spraying agents.
U.S. Pat. No. 7,482,058 B2 discloses a method of making cellulose material with improved absorbency. An absorbent cellulose material having an application of superabsorbent polymer adhered to the cellulose material, wherein an aqueous solution of pre-superabsorbent polymer is applied to the cellulose material and converted to superabsorbent polymer upon subjecting to a sufficient time. The absorbent cellulose material has a fluid retention of greater than 2 g/g.
U.S. Pat. No. 5,372,877, describes a method of producing a biodegradable cushioning product which may include cellulose fibers from waste paper, in which superabsorbent polymers such as starch graft copolymers and/or modified hydrophilic polyacrylates were added. In this method, around 10% of a water soluble adhesive is used. Porous foam materials made from aerocellulose gels were reported (2006) through drying the gels in supercritical conditions so that the openness of the gel structure is largely maintained.
A method to produce a natural fibrous foamed product is described in CN1912247A (2007) and WO 2012/006714, where the alkaline treated fiber is used as a key component to form the three dimensional foamed fibrous composites panel. The process method includes multiple steps, where the 1st step is the preparation of alkaline fiber at high temperature and pressure, followed by a protracted washing process until a desired pH value for the alkaline fiber. This step requires many hours of work. The 2nd step of the process is a multiple foaming step to make the foamed fibrous materials, which included fiber presoaking, fiber disintegrating, adding adhesives and surfactants, and foaming, with the addition of certain foaming agent. The foaming process requires up to 4.5 hours to produce the foam. The process includes a further 8 to 20 hours for the drainage and the drying process for the products described in the disclosure.
There remains a need for an efficient continuous foaming process for fiber composite materials, using a simplified and scalable foaming apparatus and drying process, for the production of the ULDC products in an industrially viable manner.